Propeller blade



July 27, 1937. 1 J MASCUCH ET AL 2,087,919

PROPELLER BLADE Filed Aug. 50, 1953 I V EN TORS' dost-Pm! M l zsc UCH 45/746 R Roan MN A TTORNEY Patented July 27, 1937 UNITED STATES PATENT OFFlCE PROPELLER BLADE of New Jersey Application August 30, 1933, Serial No. 687,408

1 Claim.

This invention relates to the production of hollow metal articles of irregular shapes by electrodeposition. The invention is described as applied to the production of propeller blades for aircraft, but it is intended that other metal objects may be produced by the method herein described.

Hollow metal propellers are most desirable for aircraft use. Metal propellers are more durable than other types of propellers in that the surface will not readily break down or disintegrate by exposure to the elements when in use. Furthermore, a metal propeller is stronger than other types such as wood or wood and metal. In the event of accident a metal propeller may merely bend, in which event it may be straightened, rebalanced and reused, whereas, under similar conditions a wood or wood and metal propeller would break and would be a complete loss. propeller is desirable in order to reduce weight. A hollow steel propeller blade will either be lighter or more efficient than solid blades of any other material for most applications.

Therefore, one object of the invention is to provide a hollow metal propeller blade.

To withstand the stresses set up the metal must be hard and tough and not subject to breakage. For this reason blades made of sections joined together are undesirable since the stresses are localized at the joints, resulting in increased likelihood of breakage. Therefore, a further object of the invention. is to provide a hollow metal propeller blade of a hard metal which will be a homogeneous structure free from scams or welds.

Where metal propellers are used they are subject to surface pitting and other breakdowns by reason of lack of strength in the metal. Therefore, a further object of the invention is to produce a metal which may be formed into a propeller blade which will have an ultimate tensile strength of approximately. 150,000 pounds per square inch. Such a metal will withstand the stresses of service without breakdown.

By reason ofthe contour necessary for eflicient operation it is impracticable if not impossible to form a hollow blade from hard steel. Where soft steel is used the blade must be subsequently heat treated to impart the desired physical properties A hollow using an air-hardening steel alloy of sufilcient tensile strength and forming the blade by electro-deposition. Therefore, a further object of the invention is to produce a hollow propeller blade by electro-deposition of an iron alloy which may be subsequently heat-treated to provide the desired carbon content and other physical properties, to produce an air-hardening steel.

Since it is desirable to produce a propeller in which the'thickness of the metal will vary from the tip to the base or shank, it is a further object of the invention to provide means to vary' the thickness of the deposit in making the blade.

A further object of the invention is to provide a method for producing a hollow metal propeller blade by electro-deposition.

A further object of the invention is to provide a plating bath from which may be deposited a blade of an alloy having the desired qualities.

The invention consists of the combination of elements, the steps of the method and process, and the article produced, by performing the steps of the method and process, as herein illustrated, described and claimed.

In the accompanying drawing forming part hereof, is illustrated a propeller formed by depoand,

Figure 3 is a section on line 3-3 of Figure 1.

Referring to the drawing, 5 designates the wall of a hollow blade of a continuous piece of metal having an inner surface 6; l designates a base or shank which is fitted into a hub 8.

To make the blade a mold is formed, the inner or molding surface of which will have the exact contour of the inner surface of the blade to be produced. The mold may be made of any well known materials suitable for the purpose. A core is then cast in the mold, which core, when removed from the mold, will have the same shape as the inside wall 6 of the blade 5. The core may be cast with a threaded nipple extending from the shank end which nipple may be secured to a supporting member to hold the core in position in the plating solution. The core may be of wax or other suitable material, or it may preferably be cast of any suitable metal or alloy having a melting point lower than the alloy to be deposited thereon. As an alternative,

of a mold but where the core is made of metal it is desirable to cast it. If the core is made of non-conductive material it is treated by applying graphite or metal powders thereto to render it conductive. I

The core is then made the cathode in a plating bath more fully described hereinafter, and a covering of metal is deposited thereon. The deposition is continued until the desired thickness of metal is deposited on the core.

Sinceit is desirable that the thickness of the wall 5 increases from the tip of the blade to the base 1, the core may be placed in the bath with the tip upward and the core gradually and continuously raised from the solution, or the level of the solution may be continuously lowered. If it is not desired to do this there may be inserted in the solution a conductor so arranged with respect to the core that it receives the deposit and locally depletes the metal ion concentration and thereby locally reduces the rate of deposit on the desired part of the core surface.

When the deposited metal has attained the desired thickness the blade is removed from the bath, the core melted out through the nipple in the base or shank I, and the nipple removed, leaving the hollow blade 5. The blade is then machined to make it perfectly smooth and the shank l shaped to be fitted into a hub. When this has been done the blade is balanced. The blade is then packed inside and out with wood and bone charcoal, or other suitable materials and carburized in accordance with common practice, to impart the desired carbon concentration andother properties to the blade. After carburizing the blade it is air-hardened. After the blade has been air-hardened it is checked to insure that the proper balance has been maintained and is rebalanced, if necessary. A pair of balanced blades 5 are then fitted to a hub 8 and the propeller is complete.

It is desirable to produce the blade of -a hard steel alloy. A nickel steel alloy has been found to give very satisfactory results but other alloying elements such as manganese, chromium, tungsten, vanadium and molybdenum may be used with iron to produce a steel having the desired qualities. The use of nickel steel is described herein to illustrate the invention. The invention is not limited thereto since by variations in the process, which may be readily ascertained by one skilled in the art, alloys of different metals may be produced.

It is a well known characteristic of solutions of ferrous salts that they will precipitate basic iron compounds, as for example ferric hydroxide, if they are exposed to the air or if the hydrogen ion concentration, hereafter called pH, is less than approximately 3.0. This tendency toward the oxidation and/or hydrolysis of these ferrous solutions will be greatly retarded by the addition of a base-forming element ore negative than iron, as for example, calcium. It has been found that this hydrolysis occurs more rapidly in. hot than in cold' solutions and that its presence results in seriously roughened deposits. However, it is desirable to use boiling solutions and it is therefore essential that extra precautions be exercised to prevent the aforesaid hydrolysis. Calcium chloride of concentration such that the boiling point of the solution will occur at'from 106 C.

to 110 C. will accomplish the desired result. A solution of this concentration and at a pH determined by other characteristics will not only 2,087,919 the core may be made directly without the use prevent the hydrolysis but will redissolve any basic iron salts which may have formed. As an example of the foregoing it'has been found that a boiling solution containing 20 grams per liter of iron as ferrous chloride in which there is a turbidity due to ferric hydroxide, requires that the pH be lowered to 1.6 before the hydroxide will redissolve. But, upon the addition of calcium chloride to the concentration as above stated the ferric hydroxide will dissolve at a pH of 2.4. For reasons which will later be set forth it may be desirable to operate the solution within the range of 1.6 to 2.4 with an iron concentration of approximately 20 grams per liter, and it is therefore essential to use this concentration of calcium chloride or its equivalent.

The process is not restricted to the use of calcium chloride as it has been found, as the voltage across an alloy bath is reduced the more noble metal is deposited in increasing proportion, until below some critical current density, it may be of an undesirable, black, amorphous character, and that any base-forming element with an anion common to the anion or radicle used with the iron will accomplish the desired result provided such a salt is sufiiciently soluble, as for example the combination of ferrous sulphate and magnesium sulphate. The concentration with boiling point 106 to 110 C. is correct for the combination ferrous chloride-calcium chloride,

the proper concentration may readily be determined for other combinations by anyone versed in the art, and as they are quite numerous the disclosure is confined to the afore-mentioned chloride combination, but it is to .be understood that the other combinations are equally effective.

Iron being a base metal connot be deposited from acid solutions without the evolution of hydrogen from the cathode. This is not serious in the case of a straight iron deposit but it has been found that serious pitting, due to the hydrogen, will occur when depositing iron and an alloying element, as for example, nickel. Several theories have been advanced to account for this fact, none of which are completely satisfactory, but it has been found that in a boiling bath the trouble is completely eliminated and no other method has been found which is as completely effective as boiling for the elimination of this pitting trouble.

This boiling, however, introduces other complications which must be provided for. As stated above, the greater hydrolysis of hot solutions must be retarded by the use of a base-forming common anion salt. The loss of throwing power due to the violent agitation may be minimized by the reduction of the metal ion concentration which will be described later. But it has been found that as current densities of any alloying element having the same anion but more electropositive, as for example, ferrous chloride and nickel chloride, there is a critical point at which the alloying element will alone be deposited and the deposit will be amorphous.

By experiment it has been determined that as the metal ion concentration is reduced this critical point becomes lower and lower, and by further experiment it has been found that for each combination there is a pH value at which the critical point falls below the usable range of current densities and therefore is no longer objectionable. This determines the low pH limit.

Exhaustive experiments have shown that there are certain fixed limits beyond which the constituents of the solution may not vary in order to produce the desired alloy. It has been found that iron in the form of ferrous chloride may be varied between and 20 grams per liter of water, and the nickel in the form of nickelous chloride between 1 and 4 grams per liter of water. calcium chloride may vary between 200 and 500 grams per liter of water and the pH of the solution, which is produced by adding hydrochloric acid, may vary between 1.0 and 3.0. In operation the current density may vary between 20 and 100 amperes per square foot. In the solution is placed an iron anode and a nickel anode, the wet area of the nickel anode being from 2 to 5 times greater than the wet area of the iron anode, or a single alloy anode may be used. Their relative wet areas, being adjusted to maintain a constant metal ratio in the bath, or a single alloy anode may be used, or iron anodes alone the wet area of the iron anode.

This solution produces an alloy deposit capable, by suitable treatment, of being converted into an air-hardening steel of approximately 8% nickel and 92% iron.- When carburized to provide a relation to the. ferrous chloride in the solution may be increased, or the current density may be decreased; or, the pH may be increased. As long as the.variations are kept within the limits set forth above a suitable alloy may be produced, conversely', the nickel content of the deposit may be reduced. Of course, the greater the nickel content the less carbon concentration will be needed The to produce a steel having a tensile strength sufliciently high for use in propellers.

The degree of hardness of the metal will depend to a certain extent upon time and temperature of the heat treatment in'carburizing the alloy. The blade or other article may be cooled in the carburizing box in the furnace, or it may be cooled in freely circulating controlled air. Since variations in time and temperature are well known in assisting to control the hardness of metals, it is not deemed necessary, to set forth a table of hours and temperatures to produce metals of different carbon content.

We have discovered that for any chloride solution of iron, nickel and calcium there is some pH at which the percentage of nickel in the deposit is independent of current density at all current densities above the immediate neighborhood of the critical current density. Since there are variations in current density distribution on irregularly shaped cathode or in fact, on any cathodes with comparatively sharp edges or corners, the alloy deposit would vary as a function of this distribution; that is, if an iron nickel bath were operated at a pH above the value at which the percentage of nickel is independent of current density, all parts of the cathode which receiv the high current density, such as edges and corners, wouldcontain a lower amount of nickel than the flat central portion of the cathode.

Since it is important to have uniform nickel concentration in all parts of the deposit in order that all parts will respond uniformly to heat treatment and have uniform physical properties, we will invariably operate our baths at that pH at which the curve of percentage of nickel in the deposit plotted against current density is straight and horizontal at current densities above approximately 30 amperes per square foot.

Having thus fullydescribed the invention, what is'claimed as new and desired to be secured by Letters Patent is:

A hollow, one piece aircraft propeller blade free of scams or welds formed of an air hardening alloy nickel steel of uniform hardness and having a tensile strength of at least one hundred fifty thousand pounds per square inch.

- JOSEPH J. MASCUCH.

ISAAC P. RODMAN. GLEN T. LAMPTON. 

